Low emissivity coatings for transparent substrates, such as automotive and architectural glazing, are known to those skilled in the art. Likewise, coated glazing products having anti-solar properties, that is, low transmittance of wavelengths in the infra-red range, also are known to those skilled in the art. Low emissivity coatings for glazing products are disclosed, for example, in European patent application 0,104,870 to F. H. Hart entitled Low Emissivity Coatings On Transparent Substrates. That document discloses low emissivity silver coatings comprising a layer of silver and an overlying anti-reflective layer of metal oxide. Cathodic sputtering is disclosed for producing such low emissivity coatings having a small amount of an additional metal dispersed non-uniformly in the silver layer. Sputtered deposition of a multi layer low emissivity coating is described, for example, in European Patent Application 0,418,435 to Nalepka. Similarly, a multi-layer low emissivity coating is disclosed in European patent application 0,418,435 to Hayward et al. The multi-layer coating of Hayward et al. is said to comprise a layer of sputtered zinc, tin, titanium, indium/tin or bismuth oxide, next a layer of sputtered silver or silver alloy, then a layer sputtered titanium or stainless steel and finally a layer of zinc, tin, titanium, indium/tin or bismuth oxide. Such multi-layer film is said to have excellent visible light transmission while controlling both near infra-red solar energy and far infra-red reflected energy. A temperable coated article is suggested in U.S. Pat. No. 5,552,180 to Finley et al. The coated article of Finley et al. employs a metal-containing film such as titanium nitride which ordinarily oxidizes at the high temperatures encountered during glass tempering, along with an overcoating of a protective layer of a silicon compound and an undercoating with a stabilizing metal-containing layer. In U.S. Pat. No. 3,990,784 to Gelber a multi-layer coating for architectural glass is suggested, comprising first and second metal layers with a dielectric layer disposed between them. Gelber suggests that the transmission properties of the coating can be changed independent of its reflection properties, by varying the thickness of the metal layers while maintaining the ratio of their thicknesses constant.
In general, conventional low emissivity coating systems employ a first dielectric film or layer directly on a surface of a transparent substrate, followed by metal film and then a second dielectric film over the metal film. Where the metal film employs silver or other easily oxidized metal, a buffer film typically is positioned between the metal and the second dielectric films. The buffer film substantially inhibits migration to the metal film of oxygen or other reactive gas employed in the deposition of the second dielectric film. Conventional dielectric materials include, for example, oxides such as zinc oxide, tin oxide, zinc/tin oxide composites, indium/tin oxide, bismuth oxide, titanium oxide, etc., and nitrides such as tin nitride. The metal layer frequently employs silver, although other metal layers also are known to those skilled in the art. Suitable buffer layers for protecting a silver or other metal film have typically been, for example, a sub-oxide of chrome or chrome/nickel or nitride of silicon or titanium film 100.ANG. to 120.ANG. thick. The thickness of the metal film is selected to provide adequately low emissivity while maintaining sufficiently high transmittance of visible light to meet the requirements of the intended application. The thickness of the bottom and top dielectric films is selected typically to achieve adequate anti-reflectance for the metal film, whereby the entire multi-layer coating has improved transparency to visible light.
Various difficulties have been encountered by those skilled in the art in developing commercially suitable coatings for architectural and automotive glazing. In particular, it has proved difficult to achieve low emissivity coatings which also provide good attenuation of direct solar radiation, that is, good anti-solar properties. There has long been need in the glazing industry for coating systems which can be uniformly deposited by sputtering onto large surface areas with fast deposition rates, low deposition power density, good film quality, including high film durability, bulk or near bulk density, and long shelf life. As used here, large area deposition refers to deposition onto transparent substrates suitable in size for architectural and automotive glazing applications. Fast deposition rate is desirable, since it can reduce the time and cost of producing the coated articles. Long lasting source material to deposit reproducible films is desirable. Low deposition power density is desirable both to reduce the cost of energy employed in manufacturing the coated article and to provide more uniform coating thickness and density. The reference here to a multi-layer coating having long shelf life is intended to mean, especially, that the coated surface can be exposed to air for hours or even days without substantial degradation of film quality, for example, due to migration of oxygen or moisture from the air into the coating to react with the coating materials. In that regard, substantial manufacturing process complexity and production wastage occurs when the sputtered multi-layer coating on a glazing panel deteriorates significantly if it is not immediately laminated or otherwise assembled into a multi-pane window which protects the coating from exposure to air. Increasing the time period during which a coated glazing panel can be stored prior to being laminated or assembled in this fashion provides significant production flexibility with consequent reduction in processing cost and complexity. Easily degrading deposition sources increases the production costs. Large area processable materials/processes are also desirable.
It is an object of the present invention to provide coated articles meeting some or all of these long-felt industry needs. In particular, it is an object of at least certain preferred embodiments of the invention to provide coated articles of manufacture comprising a substantially transparent substrate with a substantially transparent coating of the surface of the substrate, which coating has high film durability, bulk or near bulk density and long shelf life.
It is a particular object of the invention to provide coated articles comprising a transparent substrate having a double functioning multi-layer coating on at least one surface of the substrate. Such coating providing both low emissivity and anti-solar performance characteristics. In accordance with certain preferred embodiments, it is a further object to provide glazing units and electrically conductive panels.
It is a further object of the invention to provide methods of manufacturing the aforesaid coated articles.
Additional objects and advantages of the present invention will be readily understood by those skilled in the art given the benefit of the following disclosure of the invention and detailed description of preferred embodiments.